Phased array technology is rapidly advancing and targeting a number of applications in the millimeter-wave/sub-THz ranges. Examples of such applications include satellite communications, automotive radar, 5G cellular communications, imaging and sensing. This type of applications makes use of antennas with beam-steering capability which can be realized with phased array antennas. High performance integrated phase shifters are important components in the millimeter-wave/sub-THz phased array antenna systems.
Beam-steering focuses the electromagnetic energy in a specific direction, which may be used to increase the signal to noise or interference ratio, reduce the system overall power consumption and/or increase the channel throughput. Beam-steering in phased array is mainly achieved by the phase shifters which introduce progressive linear phase difference between antenna elements. Depending on the relative values of these phase shifts the antenna beam responds by being steered towards a specific direction.
The main drawback of utilizing passive phase shifters in such applications lies in the fact that the insertion loss changes remarkably with the introduced phase shift. Higher insertion loss variation leads to a significant distortion of the radiation pattern while the beam is being steered. Using variable gain amplifiers/attenuators to compensate for the change in the phase shifter insertion loss is one way to solve this problem; however, this approach adds to the design complexity, overall cost, power consumption and/or noise level of the integrated system.
For active phased arrays with a high precision beam pointing, each individual antenna element may be integrated with its own phase shifter. This imposes a stringent size constraint on the total foot print of the phase shifting element. For example, for Ka-band phased arrays operating at a frequency of 30 GHz, each phase shifter with its active and passive peripherals may occupy only an area of less than 5 mm*5 mm. Commercial phased array systems also desire low cost integration and fabrication. The size limitation and the lack of a low cost packaging solution for mass-production in some existing solutions make them difficult for the use of large commercial phased arrays.